Electron spin resonance for medical imaging

ABSTRACT

A method includes generating, from an integrated oscillator circuit, an oscillating output signal and generating, by an integrated power amplifier (PA) circuit, an amplified oscillating output signal based on the oscillating output signal. The method further includes receiving, by integrated receiver amplifier circuit, an electron spin resonance (ESR) signal from biological samples that include a magnetic species and generating, by the integrated receiver amplifier circuit, an amplified ESR signal based on the received ESR signal. The method further includes receiving, by the integrated receiver amplifier circuit, an electron spin resonance (ESR) signal from magnetic nanoparticles that are loaded with drugs or attached to human cells.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority, pursuant to 35 U.S.C. §119(e), to U.S.Provisional Application No. 61/707,441, the contents of which isincorporated by reference herein in its entirety.

BACKGROUND

Electron spin resonance (ESR), also equivalently referred to herein aselectron paramagnetic resonance (EPR), is a spectroscopic and imagingtechnique that is capable of providing quantitative informationregarding the presence and concentration of a variety of magneticspecies within a sample under test, e.g., a biological tissue sample.The valence electron(s) of a magnetic species possess unpaired spinangular momentum and thus, have net magnetic moments that tend to alignalong an externally applied magnetic field. This alignment process isknown as magnetization. ESR is a measurement technique that relies onthe external manipulation of the direction of this electronmagnetization, also referred to as a net electronic magnetic moment. Ina typical ESR experiment, a polarizing magnetic field B₀ is applied to asample to align the magnetic moments of the electrons along thedirection of the magnetic field B₀. Then, an oscillating magnetic fieldB₁, often referred to as the transverse magnetic field, is applied alonga direction that is perpendicular to the polarizing field B₀. Usuallythe oscillating field B₁ is generated using a microwave resonator (acoil or a transmission line) and is designed to excite the unpairedelectrons by driving transitions between the different angular momentumstates of the unpaired electron(s).

Currently there are two major techniques used to perform ESRspectroscopy. The first is a continuous wave (CW), frequency domainmethod and the second is a pulse-based, time domain technique. A CWspectrometer utilizes a continuous, narrow-band signal to create B₁ andthus, energize unpaired electrons in the presence of the external DCmagnetic field B₀. In CW spectroscopy, an absorption spectrum of thesample is obtained by either sweeping the frequency of B₁ while B₀ iskept constant or by sweeping B₀ while the frequency of B₁ is keptconstant. CW spectroscopy has been traditionally used for ESR because itis simpler in terms of circuitry and is able to detect samples even withvery fast relaxation times (tens of nanoseconds). However, directmeasurement of certain spin relaxation parameters, such as thelongitudinal relaxation time, also referred to as the spin-latticerelaxation time (T₁) and/or the transverse relaxation time, alsoreferred to as the spin-spin relaxation time (T₂) is feasible using timedomain or pulse techniques. In pulse ESR, instead of sweeping acontinuous signal, B₁ is pulsed in a precisely designed pulse sequenceto manipulate the direction of the spins of the unpaired electrons. Thesubsequent time-domain ESR signal emitted from the electrons as theyrelax back to their equilibrium state is then recorded by a receiverresonator. In pulsed ESR, wideband spectral information relating to theESR samples may be reproduced using Fourier transform techniques appliedto the ESR signal.

Presently, ESR imaging and spectroscopy are conducted using systems thatemploy a large number of discrete radiofrequency (RF) or microwavecomponents. For example, current systems employ discrete RF sources,pulse generators, power amplifiers, lock-in amplifiers, resonators,mixers, analog-to digital converters, connecting cables, etc. However,as the instrument sizes exceed the characteristic wavelengthscorresponding to the ESR experiment frequency (typically less than 1meter, corresponding to a frequency of 300 MHz) the spectrometer/imagerbecomes sensitive to radiative effects and noise from the ambient RFradiation. This results in noisy and/or unstable data. Furthermore, theweight of the magnets and the RF components is typically hundreds ofkilograms thereby prohibiting the portability of currently existing ESRspectrometers/imagers. Furthermore, the cost of building an ESR imagerfrom discrete components can be prohibitively high. Finally large,discrete ESR imagers also have slow response times. This becomes a keylimitation for time-domain imaging/spectroscopy, where the response timeof the imager determines the shortest relaxation time that can bedetected using time-domain ESR. Current in-vivo ESR imagers haveresponse times that are limited to 1 microsecond or greater.

SUMMARY

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

In general, in one aspect, one or more embodiments are directed to amethod of obtaining an electron spin resonance (ESR) signal from abiological sample using an integrated electron spin resonance circuitchip having a chip substrate. The method includes generating, from anintegrated oscillator circuit, an oscillating output signal andgenerating, by an integrated power amplifier (PA) circuit, an amplifiedoscillating output signal based on the oscillating output signal. Themethod further includes receiving, by integrated receiver amplifiercircuit, an ESR signal from the biological sample that includes amagnetic species and generating, by the integrated receiver amplifiercircuit, an amplified ESR signal based on the received ESR signal. Themethod further includes down-converting, by an integrated mixer circuit,the amplified ESR signal to a baseband signal and generating, by anintegrated baseband amplifier circuit, an amplified baseband signalbased on the baseband signal. The integrated oscillator circuit, theintegrated PA circuit, the integrated receiver amplifier circuit, andintegrated mixer circuit, and the integrated baseband amplifier circuitare all disposed on the chip substrate.

Other aspects of the invention will be apparent from the followingdescription and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-1B show an integrated electron spin resonance (ESR)spectrometer in accordance with one or more embodiments of theinvention.

FIG. 2 show an integrated electron spin resonance (ESR) spectrometer inaccordance with one or more embodiments of the invention.

FIG. 3 show an integrated programmable pulse generator circuit inaccordance with one or more embodiments of the invention.

FIGS. 4A-4C show an integrated transmitter circuit in accordance withone or more embodiments of the invention.

FIGS. 5A-5B show an integrated receiver circuit in accordance with oneor more embodiments of the invention.

FIG. 6A shows a micrograph of an integrated transceiver circuit inaccordance with one or more embodiments of the invention.

FIGS. 6B-6H show the metal layers of a multi-layer chip layout inaccordance with one or more embodiments of the invention. FIG. 6B, 6C,6D, 6E, 6F, 6G, and 6H correspond to layers M7 or AM (aluminum, toplayer), M6 or LY (aluminum), M5 or MQ (copper), M4 (copper), M3(copper), M2 (copper), and M1 (copper, bottom layer).

FIGS. 7A-7C show an integrated ESR spectrometer in accordance with oneor more embodiments of the invention.

FIG. 8 shows an active leakage cancellation circuit in accordance withone or more embodiments of the invention.

FIGS. 9A-9D shows an integrated transmitter circuit in accordance withone or more embodiments of the invention.

FIGS. 10A-10C show an integrated receiver circuit in accordance with oneor more embodiments of the invention.

FIG. 11A shows a micrograph of an integrated transceiver circuit inaccordance with one or more embodiments of the invention.

FIGS. 11B-11H show the metal layers of a multi-layer chip layout inaccordance with one or more embodiments of the invention. FIG. 6B, 6C,6D, 6E, 6F, 6G, and 6H correspond to layers M7 or AM (aluminum, toplayer), M6 or LY (aluminum), M5 or MQ (copper), M4 (copper), M3(copper), M2 (copper), and M1 (copper, bottom layer).

FIGS. 12A-12B show an integrated ESR spectrometer in accordance with oneor more embodiments of the invention.

FIGS. 13A-13B show test data for an integrated programmable pulsegenerator circuit in accordance with one or more embodiments of theinvention.

FIGS. 14A-14B show test data for an integrated voltage controlledoscillator circuit in accordance with one or more embodiments of theinvention.

FIG. 15 shows test data for an integrated transmitter circuit inaccordance with one or more embodiments of the invention.

FIG. 16 shows test data for an integrated transmitter circuit inaccordance with one or more embodiments of the invention.

FIGS. 17A-17B show test data for an integrated transceiver circuit inaccordance with one or more embodiments of the invention.

FIGS. 18A-18B show system specification for integrated transceivercircuits in accordance with one or more embodiments of the invention.

FIGS. 19A-19B show test data for an integrated transceiver circuit inaccordance with one or more embodiments of the invention.

FIG. 20 shows a method in accordance with one or more embodiments of theinvention.

FIGS. 21A-21B show test data for an integrated transceiver circuit inaccordance with one or more embodiments of the invention.

FIGS. 22A-22B show test data for an integrated transceiver circuit inaccordance with one or more embodiments of the invention.

FIGS. 23A-23B show test data for an integrated transceiver circuit inaccordance with one or more embodiments of the invention.

FIGS. 24A-24B show test data for an integrated transceiver circuit inaccordance with one or more embodiments of the invention.

FIG. 25 shows an ESR system in accordance with one or more embodimentsof the invention.

FIG. 26 shows an ESR system in accordance with one or more embodimentsof the invention.

FIGS. 27A-27B show test data in accordance with one or more embodimentsof the invention. FIG. 27A shows a detected ESR signal as a function ofdistance from the front surface of a permanent magnet. This measurementuses a fixed distance between a resonator and a sample. FIG. 27B showsthe magnetic field as a function of distance from the same permanentmagnet for purposes of calibration.

FIGS. 28A-28C show test data in accordance with one or more embodimentsof the invention. FIG. 28A shows the detected ESR signal for a varyingdistance (from 0 mm to 5 mm) between a resonator and a sample. FIG. 28Bshows the detected ESR signal for a varying distance (from 0 mm to 35mm) between a resonator and a sample. FIG. 28C shows the detected ESRsignal for a varying distance (from 0 mm to 40 mm) between a resonatorand a sample using a different resonator.

FIG. 29 shows a measured ESR signal as a function of displacement alonga direction that is parallel to a front face of the permanent magnet andperpendicular to a table surface of the test bench. Several differentseparations between a sample and a resonator are shown.

FIGS. 30A-30B show a measured ESR signal as a function of displacement(forward and backward) along a direction that is parallel to the frontface of the permanent magnet and parallel to the table surface of thetest bench. Several different separations between a sample and aresonator are shown.

FIGS. 31A-31B show results of characterization of the magnetic filedproduced by the permanent magnet used to produce the data of FIGS.27-30.

FIG. 32 show a plot of the magnetic field produced by the permanentmagnet used to produce the data of FIGS. 27-30.

DETAILED DESCRIPTION

Specific embodiments of an integrated electron spin resonance (ESR)spectrometer will now be described in detail with reference to theaccompanying figures. Like elements in the various figures (alsoreferred to as FIGURES) are denoted by like reference numerals forconsistency.

In the following detailed description of embodiments, numerous specificdetails are set forth in order to provide a more thorough understandingof integrated ESR spectrometer. However, it will be apparent to one ofordinary skill in the art that these embodiments may be practicedwithout these specific details. In other instances, well-known featureshave not been described in detail to avoid unnecessarily complicatingthe description.

In general, embodiments of the invention relate to an integrated ESRspectrometer. As used herein, the term integrated refers to a monolithiccircuit that is integrated onto a single chip substrate. Furthermore theterm chip substrate is used herein broadly to include any layer of amulti-layer integrated circuit. For example, one or more embodiments ofan integrated ESR spectrometer include a transmitter, receiver, and aprogrammable pulse generator that are formed on the same ship substrate,e.g., the circuitry may be implemented in silicon by way of a 0.13 μmSiGeBiCMOS process, or the like. In accordance with one or moreembodiments, the integrated transceiver of the ESR spectrometerdisclosed herein is capable of operating in a continuous wave (CW) modeand/or a pulse mode. In accordance with one or more embodiments, theintegrated ESR spectrometer may also include an integrated ESR probethat employs an integrated resonator for exciting and receiving ESRsignals from a sample under test. In accordance with one or moreembodiments, the integrated ESR spectrometer may also include anexternal ESR probe that employs an external resonator for exciting andreceiving ESR signals from a sample under test.

In accordance with one or more embodiments, the integrated ESRtransceiver chip includes an integrated programmable pulse generatorthat may produce RF pulses having varying durations and spacings.Programmable pulse durations are possible that have durations that rangefrom 0.5 ns to 500 ns. In addition, the integrated transmitter circuitof the integrated ESR transceiver chip may be switched off very quickly,e.g., in approximately 1 ns. This results in a spectrometer that has avery short, approximately 1 ns, dead time. As used herein, the termspectrometer dead time refers to the minimum duration of time that mustelapse between excitation and detection of the ESR signal form thesample.

This programmable pulse capability in combination with this short deadtime allows the integrated ESR spectrometer to be used for time domainESR spectroscopy as well as frequency domain ESR spectroscopy.Furthermore, the integrated ESR system may be used across a number ofdifferent frequency ranges. For example, one or more embodimentsdisclosed herein operate within a range of about 0.5-27 GHz. However,other frequency ranges may be used without departing from the scope ofthe present disclosure.

Furthermore, as used herein the terms ESR and EPR are understood to becompletely synonymous and interchangeable and thus, the use of one orthe other is not meant to differentiate between the magnetic property ofthe sample under test. In other words as used herein the terms EPR andESR are not meant to limit the type of electronic magnetic property ofthe sample, but rather are used generally to refer to the a measurementtechnique that manipulates the electronic magnetization of a sample. Asused herein the term magnetic species is used broadly to cover allmolecules, atoms, or particles with unpaired electron spins and thus,refers to all species that having a net electronic magnetic moment.Examples of magnetic species include but are not limited to para- ordia-magnetic atoms, molecules, ions, free radicals, or any type ofparamagnetic nanoparticle, or any other magnetic particle that may beused to produce an ESR signal. Accordingly, the term EPR and ESR signalas used herein to refers to a signal that originates from the magneticresonance of the species' electronic magnetic moment (or equivalentlythe net electronic angular momentum, spin or otherwise) of the species.

The integrated ESR spectrometer in accordance with one or moreembodiments may be used to measure ESR parameters such as the spin-spinrelaxation time (T₂) using RF pulse sequences having two or more RFpulses. In addition, the integrated ESR spectrometer may be used tomeasure ESR parameters such as the spin-lattice relaxation time (T₁)using inversion recovery techniques. In general, the integrated ESRspectrometer may be used to make any other type of time domain ESRmeasurement without departing from the scope of the present disclosure.In addition, by operating in CW mode, the integrated ESR spectrometermay be used to conduct frequency domain ESR spectroscopy.

In accordance with one or more embodiments, the integrated ESRspectrometer in accordance with one or more embodiments is extremelyversatile and may be used in a number of different applications. Becauseof its small size, e.g., 1 mm by 2 mm, the integrated ESR transceiverchip may be employed in a non-invasive, point-of-care (POC) instrument.For example, integrated ESR spectrometer may be part of a handheld ESRsystem that may be used to study the properties of magnetic species suchas metal ions in enzymes and/or free radicals involved in biochemicalsignaling pathways. In addition, the ESR system may be used to makedirect measurements of the partial pressure of oxygen (pO₂) in tissueswith high sensitivity and accuracy. Because pO₂ has been shown to berelated to many diseases, e.g., cancer and peripheral vascularinsufficiency, the ESR system in accordance with one or more embodimentsmay be used to diagnose disease. Furthermore, the integrated ESR systemmay be used to diagnose other diseases whose presence may be detectableusing ESR, e.g., melanoma. In accordance with one or more embodiments,the integrated ESR system may be used to image free radicals and performoximetry. Further examples of uses for the versatile integrated ESRsystem discloses herein include cancer tumor imaging and cardiacimaging. The invention is not limited to the aforementioned examples.

FIGS. 1A-1B show an integrated ESR system in accordance with one or moreembodiments of the invention. In accordance with one or moreembodiments, the system includes an integrated ESR transceiver chip 100and an ESR probe module 105. Furthermore, in accordance with one or moreembodiments, the integrated ESR transceiver chip 100 includes atransmitter circuit 101 and a receiver circuit 103. Each of thesecomponents of the system will be described in more detail below inreference to FIGS. 4-11. FIG. 1A shows the ESR system configured toperform CW ESR measurements. FIG. 1B shows the ESR system configured toperformed pulsed ESR measurements. In accordance with one or moreembodiments, both configurations may employ an RF circulator 107 suchthat the same resonator 109 may be used for both the transmission of RFpower to the sample during the excitation phase and for the reception ofthe ESR signal from the sample during the detection phase. However, oneor more embodiments of the invention may alternatively employ separateor multiple resonators for transmission and reception without departingfrom the scope of the present disclosure. In accordance with one or moreembodiments, the transmitter circuit 101 and receiver circuit 103 may belocated on the same chip substrate 100 and fabricated thereon as asingle-chip transceiver, e.g., they may be implemented in a 0.13 μmSiGeBiCMOS process technology, as described in more detail below.Furthermore, although not shown in FIGS. 1A-1B, the resonator 109 may beintegrated onto the transceiver chip 100 in accordance with one or moreembodiments.

FIGS. 1A-1B further show that the ESR probe module 105 may include amagnet 111 that generates a bias magnetic field B₀ that is capable ofbeing varied, e.g., capable of being modulated at a frequency f_(CW). Inaccordance with one or more embodiments, the magnet 111 may be asolenoid electromagnet having a spatially uniform B₀ across the sample.Furthermore, a sample 113 may be located within the magnetic file B₀ ofthe magnet 111. The probe module 105 further includes the resonator 109that may serve as a resonator for transmitting and receiving RF signals.In accordance with one or more embodiments, the resonator 109 may beintegrated into the transceiver chip 100, e.g., in the form of a planarloop-gap resonator as described in more detail below in reference toFIGS. 7A-7B. While a single resonator 109 is shown here for simplicity,one or more embodiments of the invention may employ two or moreresonators 109 that are also integrated onto the substrate 100. Such aconfiguration may or may not employ a circulator 107. When a circulator107 is employed, the RF path 121, defined as the signal path from thetransmitter to the resonator 109 that passes through ports 1 and 2 onthe circulator 107, is isolated from the ESR signal path 123, defined asthe signal path from the resonator to the receiver that passes throughports 2 and 3 on the circulator 107. Furthermore, one or moreembodiments of the invention may employ an active feedback system forincreasing the isolation between the RF path 121 and the ESR signal path123, thereby reducing the amount of RF leakage power from thetransmitter that is detected by the receiver during detection. Forexample, during CW operation, RF leakage may occur between ports 1 and 3of the circulator 107.

In an ESR measurement in accordance with one or more embodiments, themagnetic field B₀ also referred to herein as the Zeeman field, may begenerated by the magnet 111. As shown in FIGS. 1A-1B, this Zeeman fieldis present in both the CW and pulsed ESR measurements. The presence ofB₀ in the sample volume introduces an energy difference ΔE between thespin states of the unpaired electron(s) in the sample 113. The energydifference ΔE between the spin states is proportional to both B₀ and g,where g is the g-factor, a physical parameter that is dependent on theelectromagnetic microenvironment surrounding the unpaired electron.Furthermore, the sample 113 may be placed within the sample region ofthe resonator 109 so that the sample 113 is exposed to the oscillatingB₁ field generated by the resonator 109. When operating near theresonance frequency f of the resonator 109, the resonator produces astrong RF magnetic field B₁ that is perpendicular to B₀. In accordancewith one or more embodiments, the resonance frequency f is chosen suchthat hf=ΔE, where h is Planck's constant. Thus, electron transitionsbetween the spin states are possible and the RF energy generated by theresonator 109 is absorbed efficiently.

FIG. 1A shows an ESR system configured to operate in the CW mode inaccordance with one or more embodiments. In the CW mode, a sinusoidal RFsignal 115 is sent to the resonator 109 and reflected RF power 117 thatis reflected from the resonator is measured to calculate the amount ofthe RF power absorbed by the sample 113. The absorbed power varies withthe strength of the B₀ field and thus, the RF power absorption curve,reflected in the reflected RF power 117 as a function of B₀, reveals themagnetic properties of the sample 113. In accordance with one or moreembodiments, in order to reduce the low frequency noise (1/f), B₀ may bemodulated at a frequency f_(CW) and the reflected power 117 may bemeasured at the same modulation frequency f_(CW). Furthermore, inaccordance with one or more embodiments, the B₀ field may be heldconstant and the RF frequency of the sinusoidal RF signal 115 may bemodulated to perform the CW measurement.

FIG. 1B shows an ESR system configured to operate in the pulse mode inaccordance with one or more embodiments. In pulse mode, the transmittercircuit 101 sends a sequence of RF pulses 119 to the resonator 109 tomanipulate the direction of the spins of unpaired electrons of thesample 113. For example, in a spin echo measurement, a first RF pulsehaving a length T may flip the spins 90 degrees about B₀. Shortly afterthe flip, the sample may emit a free induction decay signal due to thede-phasing of the spins of the sample, which are now precessing, i.e.,rotating, about the B₀ access. Additional pulses having a duration of 2T that flips the spins by 180 degrees refocuses the de-phased spins andmay cause one or more spin echo signals to be emitted from the sample.This ESR signal, in the form of a spin echo signal, is emitted by thesample 113 and then received by the resonator 109, now operating as areception resonator. The ESR signal then travels to the receiver circuit103 by way of the ESR signal path 123. By applying a properly timedsequence of RF pulses, the timing of and number of detected spin echoescan be controlled. Of course, one of ordinary skill having the benefitof this disclosure will recognize that any type of pulsed ESRmeasurement may be employed without departing from the scope of thepresent disclosure and thus, the spin echo measurement is described hereshould not be used to limit the scope of the invention.

FIG. 2 shows an integrated ESR transceiver chip in accordance with oneor more embodiments. The integrated ESR transceiver chip 201, which mayinclude both a transmitter circuit 203 and a receiver circuit 205, isimplemented as a single chip using silicon-based fully integratedtechnology, e.g., CMOS process technology. Examples of the integratedESR transceiver chip fabricated in a 0.13 μm SiGe BiCMOS process areshown in FIGS. 6A and 11A. In accordance with one or more embodiments,the transceiver chip 201 may be implemented as part of a CW or pulsedESR system, as described above in reference to FIGS. 1A-1B. Furthermore,in one or more embodiments, a resonator 211 a may be optionallyfabricated on the same chip substrate 209 as the transmitter circuit 203and the receiver circuit 205. In other embodiments, the resonator 211 bmay be physically separable from the transceiver chip 201, e.g., theresonator 211 b may be a flat loop-gap resonator made using a printedcircuit board (PCB) such as a 20 mil Rogers 4350 B PCB, e.g., as shownin FIG. 7B. In either case, the transmitter circuit 203 includes anoscillator circuit 213 electrically connected to a power amplifier (PA)circuit 215. In accordance with one or more embodiments, the oscillatorcircuit 213 is configured to generate an oscillating output signal, alsoreferred to herein as RF power, that is then amplified by the PA circuit215 and output by the PA circuit 215 as an amplified oscillating outputsignal. The amplified oscillating output signal is then provided to theresonator 211 a (211 b) for use in an ESR measurement, e.g., the pulsedor CW measurement as described in more detail above in reference toFIGS. 1A-1B. Accordingly, the amplified oscillating output signal isapplied to a sample 212 in order to manipulate the electronic magneticmoments (or spins) of the sample 212 thereby causing an ESR signal thatis detectable by the resonator 211 a (211 b). In one embodiment, the ESRsignal may be in the form of a reduction in the amplified oscillatingoutput signal that is reflected from the resonator 211 a. In anotherembodiment, the response may be in the form of an ESR signal that isradiated, or emitted, from the sample and later detected by theresonator 211 a (211 b), e.g., the ESR signal may be a free inductiondecay signal, an inversion recovery signal, a spin echo signal, or anyother type of ESR signal.

In accordance with one or more embodiments, the receiver circuit 205 ofthe integrated ESR transceiver chip is configured to receive the ESRsignal from the sample by way of the resonator 211 a (211 b) which maybe configured in full duplex mode using a circulator as described abovein reference to FIGS. 1A-1B. In other embodiments, the resonator 211 a(211 b) may include two or more resonators that are designed asdedicated transmitter and receiver resonators. An example of this typeof multi-resonator design is shown in FIGS. 12A-12B. In accordance withone or more embodiments, the receiver circuit 205 includes a receiveramplifier circuit 217 that is electrically connected to a mixer circuit219 that is itself electrically connected to both the oscillator 213 oftransmitter circuit 203 and a baseband amplifier circuit 221. Inaccordance with one or more embodiments, the receiver amplifier circuitmay be implemented as a low noise amplifier (LNA). However, the receiveramplifier circuit need not be limited by a precise noise figure (NF)and, depending on the design constraints, the required noise figure mayvary without departing from the scope of the present disclosure. Inaccordance with one or more embodiments, the mixer circuit receives anamplified ESR signal from the LNA circuit 217 and an local oscillator(LO) signal from the transmitter circuit 203 and down-converts theamplified ESR signal to a baseband signal that may be subsequentlyamplified by the baseband amplifier circuit 221. In accordance with oneor more embodiments, the amplified baseband signal may be sent to a dataacquisition system (DAQ)(not shown) for further processing, storage,and/or display.

In accordance with one or more embodiments, the transceiver chip 201further includes an integrated programmable pulse generating (PPG)circuit 219 that is also fabricated on the same chip substrate 209 asthe transmitter and receiver circuits. Furthermore, the PPG circuit 219may be electrically connected to the PA circuit 215 and/or theoscillator circuit 213 and configured to switch the output of thetransmitter circuit 203 by switching the oscillator circuit 213 and/orthe PA 215, e.g., to perform pulsed ESR experiments.

One or more embodiments of the integrated programmable pulse generating(PPG) circuit is shown in FIG. 3. The PPG 301 is capable of producingdigital pulses with pulse widths ranging from 0.5 ns-500 ns and isintegrated onto the chip substrate along with the transmitter andreceiver circuits as shown, e.g., in the micrographs of FIG. 6A and FIG.11A. In accordance with one or more embodiments, the pulse width isdetermined by the time it takes for the capacitor 305 to discharge fromthe supply voltage V_(DD) to a threshold voltage. The “Set” signal 307is derived from an external clock signal and charges the capacitor 305on falling edges through the pull-up PMOS transistor 309 and dischargesthe capacitor 305 through the current sources 311 a, 311 b, 311 c, . . ., 311 n on rising edges. In accordance with one or more embodiments, tenbinary scaled current sources may be used, each representing a digitalbit, to control the rate at which the capacitor discharges and totherefore control the pulse width. However, any number of currentsources may be used without departing from the scope of the presentdisclosure. In accordance with one or more embodiments, the pulse widthcan be adjusted with a resolution of 490 ps. In accordance with one ormore embodiments, the discharge path through the current sources iscontrolled using a double switch design that employs a first set ofswitches 317 a, 317 b, 317 c, . . . , 317 n controlled by the set signaland a second set of switches B[0], B[1], B[2], . . . B[n] that are usedto control the number of currents sources used for the discharge path,thereby setting the pulse width. Furthermore, the PPG 301 employs acomparator-NOR logic gate on the output that includes comparator 313coupled to NOR gate 315. Test data showing output pulses of the PPGrelative to the clock Set signal are shown in FIGS. 13A-13B. As seenfrom the data in FIG. 13B, the PPG can output pulses ranging from a fewns to a few hundred ns.

In what follows, FIGS. 4-8 describe an integrated ESR system inaccordance with one or more embodiments of the invention. In theseembodiments, the system is designed to operated in both pulsed and CWmodes and to operate over a frequency range of 770 MHz to 970 MHz. Sucha system may be implemented, e.g., in a handheld device and may be usedin a wide range of non-invasive point-of-care (POC) applications, e.g.,to image free radicals and/or perform oximetry. In accordance with oneor more embodiments, the ESR system may be implemented as shown in FIG.2 using an integrated ESR transceiver chip connected to an externalresonator.

FIGS. 4A-4B show an integrated transmitter circuit in accordance withone or more embodiments of the invention. FIG. 4A shows a diagram of atransmitter circuit 401 that is suitable for an ESR spectrometer inaccordance with one or more embodiments of the invention. Thetransmitter circuit 401 includes a voltage controlled oscillator circuit(VCO) 403, a VCO buffer circuit 405, an RF buffer circuit 407, and apower amplifier circuit (PA) 409. In accordance with one or moreembodiments, the VCO 403 provides an oscillating signal having a voltagetunable frequency. The output of the VCO 403 is buffered by the VCObuffer circuit 405 and the RF buffer circuit 407. In accordance with oneor more embodiments, the VCO buffer circuit 405 ensures that theoscillation frequency of the VCO 403 remains unchanged by keeping theVCO 403 load impedance constant during the transition from excitationphase (PA on) to detection phase (PA off). In this example, the VCObuffer circuit 405 is located between the output of the VCO 403 and theLO input of a mixer (not shown) used in the receiver, as described inmore detail below. In accordance with one or more embodiments, theoutput of the transmitter circuit 401 is switched by switching the PAcircuit 409 rather than switching the VCO. Furthermore, the switching ofthe PA circuit 409 is accomplished not by switching V_(DD) but rather,by pulling down the bias voltage of an input transistor of the PA asdescribed in more detail below in reference to FIG. 4B. Accordingly, theoscillating output signal of the transmitter may be very quickly turnedon and off, i.e., it may be pulsed by providing pulses to the PA fromthe on-chip PPG, e.g., the PPG shown in FIG. 3. In accordance with oneor more embodiments, the integrated transmitter may be switched inapproximately 1-2 ns, thereby enabling pulsed ESR experiments to beperformed with the system.

FIG. 4B shows the topology of an integrated transmitter circuit likethat shown in FIG. 4A in accordance with one or more embodiments of theinvention. VCO circuit 403 is connected to the PA circuit 409 that maybe implemented on the ESR transceiver chip in accordance with one ormore embodiments. The VCO circuit 403 adopts a fully differentialnegative resistance structure with an LC tank. The frequency of this VCOis determined by the LC tank resonance frequency. The application of avoltage V_(tune) to the tuning terminal 413 of the VCO results in afrequency that can be tuned from 770 MHz to 970 MHz, as shown in thetest data of FIG. 14A. In accordance with one or more embodiments, thefrequency is tuned by applying V_(tune) as a bias voltage on the twovaractors 415 and 417 that are placed in parallel with the LC tank. Asymmetric inductor 419 is used to improve the symmetry of the device. Asthe PN-junction capacitance reduces for an increasing negative bias, theVCO frequency will be increased as V_(tune) increases. However, becausethe capacitance of varactors 415 and 417 are comparatively small,parallel fixed value capacitors 421 and 423 are used to further bringdown the frequency to approximately 1 GHz. In accordance with one ormore embodiments, the VCO signal is amplified by a differential buffercircuit 425 and is converted to a single-ended signal by signalconverter 427. FIG. 4C shows one example of an integrated signalconverter circuit 427 in accordance with one or more embodiments. Thesingle-ended VCO signal is then fed to an on-chip PA circuit 409 foradditional amplification. In accordance with one or more embodiments,the on chip PA circuit 409 has a cascode topology and provides a powergain of 15 dB. Furthermore, the output of the PA is matched to 50Ω by acombination of on-chip inductors and capacitors 429. While the VCO shownin FIG. 4B employs a fully differential negative resistance structurewith an LC tank, any type of VCO structure may be employed withoutdeparting from the scope of the present disclosure. Likewise, while thePA shown in FIG. 4B employs a single ended cascode structure, any typeof PA structure may be employed without departing from the scope of thepresent disclosure.

In accordance with one or more embodiments, the transmitter circuit 401may be operated in both CW and pulsed mode. Because the time scale fortuning off the VCO 403 is too slow for the demanding speed requirementsof pulsed ESR, the transmitter circuit 401 in the integrated ESRtransceiver is switched by switching off the PA circuit 409 whileleaving the VCO 403 in the on state. In accordance with one or moreembodiments, the PA circuit 409 may be turned off by pulling down thebase voltage of its input transistor 431 using an N-channelmetal-oxide-semiconductor field effect transistor (NMOSFET) driver 435.Generally speaking, for a pulse mode ESR spectrometer, the speed atwhich the transmitter may be switched off determines the dead time ofthe spectrometer (i.e., the minimum wait time before which ESR signalsmay be received from the sample). Since the ESR signal is usually muchweaker than the RF excitation signal, it can only be detected afterswitching off the transmitter circuit 401. The amplitude of the ESR echodecays exponentially with wait time, and therefore, a small turn-offtime is extremely important in the pulsed mode measurements. However, byemploying the design shown in FIG. 4B, the transmitter may be switchedoff very quickly by using a high speed pull down circuit formed from theNMOSFET driver 435. In this example, the NMOSFET driver 435 is used toquickly pull down the base voltage of the input transistor 431. Morespecifically, when V_(pulse) outputs a low voltage (e.g., approximately0.1V), the transistor 435 is off. Therefore, the bias of transistor 431depends only on the voltage V_(b1) and the PA is in the on state. Then,if V_(pulse) is a high voltage (e.g., approximately 1V), transistor 435is turned on and thus, reduces the bias of bias of transistor 431. Thesize of transistor 435 is chosen so that when transistor 435 is on, thebias of transistor 431 is close to 0V and well below the thresholdvoltage of transistor 431. Accordingly, in the one or more embodimentsthat employ the switching design shown in FIG. 4B, the transmitter maybe turned off in less than 1.2 ns thereby facilitating pulsed ESRmeasurements to be made using the integrated ESR transceiver chip. FIG.15 shows test data for a turn off characteristic of the transmittercircuit 401 in accordance with one or more embodiments.

FIG. 5A shows an example of an integrated receiver circuit that may beemployed as the receiver circuit in an integrated ESR transceiver shipin accordance with one or more embodiments. The receiver circuit 501includes a low noise amplifier circuit (LNA) 503, a mixer circuit 505,and a baseband amplifier circuit 507. In accordance with one or moreembodiments, the input of LNA circuit 503 is electrically connected tothe resonator (not shown) and receives an ESR signal from sample (notshown) that is located in, or near, the resonator. The output of the LNAcircuit 503 is electrically connected to the RF input port of the mixercircuit 505. Furthermore, as described above, the LO input port of themixer circuit 505 is electrically connected to the VCO thereby providingthe LO signal for the down conversion of the ESR signal to the basebandfrequency. Furthermore, the IF output port of the mixer is electricallyconnected to the input terminal of the baseband amplifier circuit 507.Thus, after being amplified by the LNA circuit 503, the ESR signal isdown-converted to baseband frequency and the baseband signal is thenamplified by the baseband amplifier circuit 507. In accordance with oneor more embodiments, the amplified baseband signal may be output to adata acquisition system (DAQ)(not shown). In accordance with one or moreembodiments, any type of data acquisition system may be used withoutdeparting from the scope of the present disclosure.

FIG. 5B shows the topology of an integrated receiver circuit like thatshown in FIG. 5A in accordance with one or more embodiments of theinvention. A direct-conversion architecture is adopted that includes LNAcircuit 503, mixer circuit 505, and baseband amplifier circuit 507. TheESR signal from the sample is coupled to the input 509 of the LNAcircuit 503. This signal is down-converted by the mixer circuit 505 andamplified by the baseband amplifier circuit 507. This amplified basebandsignal is then sent to the DAQ for analysis. In accordance with one ormore embodiments, the LNA circuit 503 has three stages and it isdesigned to have a power gain of 40 dB and a noise figure of 3.6 dB overthe entire frequency range of the VCO. The LNA output 1 dB compressionpoint is −15 dBm. Furthermore, in the physical layout of the LNA, aguard-ring with substrate contact may be used to prevent the substratecoupling from the transmitter to the receiver. While a three stage LNAis shown here as an example, one of ordinary skill will appreciate thatany number of stages and topologies may be used for the LNA withoutdeparting from the scope of the present disclosure.

In accordance with one or more embodiments, the mixer circuit 505 has aGilbert topology with a resistive load, as shown in FIG. 5B. Inaccordance with one or more embodiments, because the LNA issingle-ended, only one transistor 511 in the mixer takes the output ofthe LNA and the other transistor 513 is tied to the same DC voltage. Inaccordance with one or more embodiments, the mixer may feed to a twostage baseband amplifier circuit 507. In a CW ESR measurement, the ESRsignal after the mixer has a low frequency in the kHz domain and thus,DC block capacitors cannot be used after mixer for biasing purposes.Therefore, the first stage of the baseband amplifier may be adifferential source-follower that serves to shift the DC voltage of themixer output. The second stage may then be a common source amplifierwith output matched to 50Ω. While the mixer shown in FIG. 5B employs theGilbert topology with a resistive load, any type of mixer topology maybe employed without departing from the scope of the present disclosure.Likewise, any topology for the baseband amplifier may be employedwithout departing from the scope of the present disclosure.

In accordance with one or more embodiments, the integrated ESRtransceiver chip includes an integrated PPG as shown in FIG. 3, anintegrated transmitter as shown in FIG. 4A-4B, and an integratedreceiver as shown in FIG. 5A-5B all located on the same chip substrate.As mentioned above, each of these components may be implemented insilicon, e.g., by way of a 0.13 μm SiGe BiCMOS process, or the like. Tothat end, FIG. 6A shows a micrograph of the fabricated integrated ESRchip that includes the on-chip transmitter (VCO, buffer, and PA),receiver (LNA and mixer), and PPG circuits described above in referenceto FIGS. 1-5. In this example the chip size is 2.5 mm by 1.5 mm and thepower consumption of the entire chip is less than 425 mW. In addition,FIGS. 6B-6H show one example of a layout of an integrated ESRtransceiver chip, from top layer to bottom layer, respectively. FIG. 6Ashows a micrograph of one example of a fabricated integrated transceiverchip in accordance with one or more embodiments having a size of 2.5 mmby 1.5 mm.

Furthermore, FIGS. 13-19 summarize test data and operationalspecifications of an integrated ESR transceiver chip shown in FIG. 6.FIG. 14A shows the measured tuning range data for the VCO describedabove in FIG. 4B and implemented as shown in the micrograph of FIG. 6A.FIG. 15 shows a measured turn off characteristic for the transmitterdescribed in FIG. 4B that proves that the transmitter may be switchedoff in approximately 1 ns. FIG. 16 shows measured output pulse data forthe transmitter described in FIG. 4B operating in pulse mode.

As briefly described above, the integrated ESR transceiver chip may beemployed as part of an ESR spectrometer system in accordance with one ormore embodiments. FIG. 7A shows a more detailed diagram of an ESRspectrometer 701 that employs an integrated ESR transceiver chip 703like the one described above in reference to FIGS. 2-6. In accordancewith one or more embodiments, the system 701 includes a receiver circuit723, a DAQ 711, a circulator 713, and an ESR probe module 715. Theinteraction of these components is described in detail above inreference to FIG. 1A-1B. As already described in detail above, the ESRtransceiver chip 703 includes an integrated PPG circuit 705, anintegrated transmitter circuit 707, and an integrated receiver circuit709. Furthermore, as described above, the converted baseband signal isoutput to DAQ 711. In accordance with one or more embodiments, ESR probe715 of the ESR system 701 may be external to the ESR transceiver chip703. Furthermore, in accordance with one or more embodiments, the outputsignal from the transmitter circuit 707 may be sent to a planar loop-gapresonator 725 via the circulator 713. A planar loop-gap resonator 725 inaccordance with one or more embodiments is shown in FIG. 7B and may befabricated on a printed circuit board (PCB), e.g., a 20 mil Rogers 4350BPCB. In this example, the loop has an inner and outer diameter of 4 mmand 5 mm, respectively. In accordance with one or more embodiments, theloaded quality factor Q of the resonator 725 is measured to be 60 andthe resonance frequency may be tuned using one or more on-board tunablecapacitors. Furthermore, in accordance with one or more embodiments,variable capacitors may be applied in parallel and series with theresonator 725 to tune the resonance frequency and match the inputimpedance of the resonator 725 to 50Ω. FIG. 7C shows another example ofa resonator in accordance with one or more embodiments. Morespecifically, FIG. 7C shows a split-gap transmission line resonator inaccordance with one or more embodiments. Other types of resonators maybe used without departing from the scope of the present disclosure.

In accordance with one or more embodiments, the ESR system 701 mayoperate in pulse or CW mode. In pulse mode, the PPG circuit 705 may bedriven by external clock 717. In CW mode, the PPG is set so that thetransmitter is in the on-state and then the ESR signal is acquired bymodulating the B₀ field using the signal generator 719 to modulate thecurrent of the electromagnet 721 while simultaneously measuring thereflected power from the resonator 725, as described in more detailabove in reference to FIG. 1A.

In accordance with one or more embodiments, during the CW measurement,the transmitter circuit 707 and the receiver circuit 723 are both in theon state. However, because a typical circulator 713 has an isolationvalue of only 20 dB, the leakage power from the transmitter to thereceiver (e.g., through leakage from port 1 to port 3 of the circulator713) may be considerably larger than the ESR signal from the sample. Forexample, assuming the excitation signal is 0 dBm, the leakage power atthe input of the receiver is −20 dBm, while the ESR signal can be lowerthan −110 dBm. Therefore, in order not to saturate the ESR signal, theinput referred LNA IIP3 of the LNA must be higher than −20 dBm, whilethe LNA still needs to provide high gain in order to reduce the noisecontribution of the following stages in the receiver. Accordingly, inorder to relax this demanding design specification of the LNA and thereceiver, an active cancellation structure may be employed to cancel theleakage power from the transmitter, in accordance with one or moreembodiments.

FIG. 8 shows a diagram for the active leakage cancellation circuit 800in accordance with one or more embodiments. In accordance with one ormore embodiments, this active leakage cancellation circuit 800 may beemployed using discrete or integrated RF components. In this example,the oscillating output signal from the transmitter circuit 801, which isthe integrated transmitter circuit of the integrated ESR transceiverchip, is split to two parts A and B by the power splitter 803. Thesignal A goes through the circulator 805 and a small portion A′ leaks tothe point C. The signal B goes through a variable gainamplifier/attenuator (VGA) 807 and a phase shifter 809, and then arrivesat point D. The signal at point C and point D is summed at the summingjunction 811 and the summed signal is applied to the input of thereceiver circuit 815, which is the integrated receiver circuit of theintegrated ESR transceiver chip in accordance with one or moreembodiments. A power sensor 813 with high input impedance monitors thepower at the input 815 a of the receiver, as shown. In accordance withone or more embodiments, the power sensor 813 has a high input impedanceso as not degrade the matching and noise figure of the receiver circuit815. In accordance with one or more embodiments, two control signals 817and 819 are generated by the power sensor 813 to tune the VGA 807 andthe phase shifter 809 such that the power measured by the power sensor813 at the input of the receiver circuit 815 is minimized. Thus, theaction of the VGA 807 and phase shifter 809 is to provide a signal atpoint D that has the same amplitude but 180 degree phase difference fromthe leakage signal A′. The addition of this signal to the leakage signalA′ leads to a destructive interference between the two signals thatcauses a cancellation of the leakage signal A′ at the input 815 a. Inaccordance with one or more embodiments, the active cancellation circuit800 may reduce the leakage signal A′ by more than 40 dB as measured atthe input 815 a.

In what follows, FIGS. 9-13 describe a mm wave ESR system in accordancewith one or more embodiments of the invention. In these embodiments, thesystem is designed to operated in both pulsed and CW modes and tooperate over a frequency range of 22 GHz to 26 GHz. Such a system may beimplemented, e.g., in a handheld device and may be used in a wide rangeof non-invasive point-of-care (POC) applications, e.g., for makingdirect measurements of partial pressure of oxygen (pO₂) of tissue and/orto diagnose melanoma. In accordance with one or more embodiments, theESR system may be implemented as shown in FIG. 2 using an integrated ESRtransceiver chip having a resonator that is integrated on-chip.

FIG. 9A shows a diagram of a transmitter circuit 901 that is suitablefor an integrated ESR transceiver chip in accordance with one or moreembodiments of the invention. The transmitter circuit 901 includes avoltage controlled oscillator (VCO) circuit 903, a VCO buffer circuit905, a dual stage RF buffer circuit 907, a dual stage LO buffer circuit911, and a power amplifier (PA) circuit 909. In accordance with one ormore embodiments, the VCO circuit 903 provides an oscillating signalhaving a voltage tunable frequency. The output of the VCO circuit 903 isbuffered by the VCO buffer circuit 905 and the dual stage RF buffercircuit 907. In accordance with one or more embodiments, the VCO buffercircuit 905 ensures that the oscillation frequency of the VCO circuit903 remains unchanged by keeping the VCO circuit 903 load impedanceconstant during the transition from excitation phase (PA on) todetection phase (PA off). In accordance with one or more embodiments,the VCO buffer circuit 905 is located between the output of the VCOcircuit 903 and the input of the dual stage LO buffer circuit 911. Theoutput of the dual stage LO buffer circuit 911 is connected to the LOinput of the mixer (not shown) used in the receiver, as described inmore detail below. Furthermore, in this example, the dual stage RFbuffer circuit 907 is located between the output of the VCO buffercircuit 905 and the input of the PA circuit 909. In accordance with oneor more embodiments, in order to improve switching speed and switchingisolation, the output of the transmitter circuit 901 is switched byswitching the PA circuit 909 along with the second stage of the dualstage RF buffer circuit 907 rather than switching the VCO circuit 903.Furthermore, the switching of the PA circuit 909 is accomplished not byswitching V_(DD) but rather by employing NMOSFET switches connected tothe biasing nodes of the PA. In accordance with one or more embodiments,the NMOSFET switches act as a high-speed pull-down circuit, as describedin more detail below. By switching the PA in this manner, theoscillating output signal of the transmitter may be very quickly turnedon and off, i.e., it may be pulsed by providing pulses to the PA fromthe on-chip PPG, e.g., the PPG shown in FIG. 3. In accordance with oneor more embodiments, the integrated transmitter may be switched inapproximately 1-2 nanoseconds, thereby enabling pulsed ESR experimentsto be performed. Furthermore, by switching in this manner, isolationbetween the transmitter and receiver circuits of the integrated ESRtransceiver chip may be improved.

FIGS. 9B-9D shows the topology of a transmitter circuit like that shownin FIG. 9A in accordance with one or more embodiments of the invention.The transmitter circuit 901 includes a voltage controlled oscillator(VCO) circuit 903, a VCO buffer circuit 905, both shown in FIG. 9B; adual stage RF buffer circuit 907 a and 907 b, both shown in FIG. 9C; adual stage LO buffer circuit 911 a and 911 b, both shown in FIG. 9D, anda power amplifier (PA) circuit 909 shown in FIG. 9B. In accordance withone or more embodiments, the VCO topology used is a negative resistancecross-coupled transistor pair that provides the oscillator core.Differential transmission lines are used to bias the oscillator core aswell as to serve as an inductor to resonate with the VCO varactors,which are implemented using reverse-biased diodes. The VCO is followedby a single-stage buffer that isolates the VCO from the PA and itspreamplifier. The VCO signal is then routed to the RF and the LO paths,each through a two-stage buffer. In particular, the second stage 907 bof the two-stage buffer in the RF path has a switches 917 a, 917 b thatshort its base voltage to ground, providing a high level of isolationbetween the VCO and the detection coil. The PA has a similar switchingmechanism through base pull-down transistors. More specifically, fastswitching is achieved through employing NMOSFET switches 913 a, 913 b,913 c that are connected to the biasing nodes 915 a, 915 b, 915 c,respectively, of the PA. Accordingly, the NMOSFET switches act as ahigh-speed pull-down circuit. This high speed pull down circuit operatesin a manner that is identical to that described above in reference tothe pull down circuit of FIG. 4. In addition, switching the PA in thismanner provides further isolation between the detection coil (not shown)and the VCO signal. This operation allows for the VCO to remain onthroughout all stages, eliminating start-up time issues. The combinedeffect of switching the buffer 907 b and the PA 909 results in a 55 dBon/off ratio for the current on the excitation coil.

FIG. 10A shows an example of an integrated receiver circuit that may beemployed as the receiver circuit in an integrated ESR transceiver chipin accordance with one or more embodiments. The receiver circuit 1001includes a low noise amplifier (LNA) circuit 1003, a mixer circuit 1005,and a baseband amplifier circuit 1007. In accordance with one or moreembodiments, the input of LNA circuit 1003 is electrically connected tothe resonator (not shown) and receives an ESR signal from sample (notshown) that is located in, or near, the resonator. The output of the LNAcircuit 1003 is electrically connected to the RF input port of the mixercircuit 1005. Furthermore, as described above, the LO input port of themixer circuit 1005 is electrically connected to the VCO therebyproviding the LO signal for the down conversion of the ESR signal to thebaseband frequency. Furthermore, the IF output port of the mixer iselectrically connected to the input terminal of the baseband amplifiercircuit 1007. Thus, after being amplified by the LNA circuit 1003, theESR signal is down-converted to baseband frequency and the basebandsignal is then amplified by the baseband amplifier circuit 1007 andoutput to a data acquisition system (DAQ)(not shown). In accordance withone or more embodiments, any type of data acquisition system may be usedwithout departing from the scope of the present disclosure.

FIGS. 10B-10C show the topology of an integrated receiver circuit likethat shown in FIG. 10A in accordance with one or more embodiments of theinvention. The receiver circuit includes four-stage variable-gain LNAcircuit 1003, shown in FIG. 10B; and mixer circuit 1005 and basebandamplifier circuit 1007, shown in FIG. 10C. The ESR signal from thesample is coupled to the input 1009 of the LNA circuit 1003. This signalis down-converted by the mixer circuit 1005 and amplified by thebaseband amplifier circuit 1007. This amplified baseband signal is thento the DAQ for analysis. In accordance with one or more embodiments, theLNA circuit 1003 is a four-stage variable-gain LNA providing a maximumvoltage gain of 61 dB. Each stage of the LNA uses a differential cascodetopology. The LNA input matching circuit is designed to maximize the LNAgain and to provide a match to the detection resonator coil (not shown).In accordance with one or more embodiments, the mixer circuit 1005 usesa double balanced Gilbert cell topology. Furthermore, in accordance withone or more embodiments, 50Ω resistors are used to degenerate the mixerin order to improve its linearity. After being down-converted by themixer, the signal is amplified by the baseband amplifier circuit 1007.In accordance with one or more embodiments, the baseband amplifierincludes a differential stage matched to a differential output impedanceof 100Ω.

In accordance with one or more embodiments, the integrated ESRtransceiver chip may include an integrated PPG as shown in FIG. 3, anintegrated transmitter as shown in FIG. 9A-9D, and an integratedreceiver as shown in FIG. 10A-10C all located on the same chipsubstrate. As mentioned above, each of these components may beimplemented in silicon, e.g., by way of a 0.13 μm SiGeBiCMOS process, orthe like. To that end, FIG. 11A shows a micrograph of the fabricatedintegrated ESR chip that includes the programmable pulse generator, asdescribed in FIG. 3, the on-chip transmitter (VCO, VCO buffer, two-stageRF buffer, two-stage LO buffer, and PA), receiver (4-stage LNA, mixer,and BB amplifier), and an integrated (on-chip) resonator. In thisexample the chip size is 2 mm by 1 mm and the power consumption of theentire chip is less than 385 mW. In addition, FIGS. 11B-11H shows thelayout of the layers of the chip, from top layer to bottom layer,respectively, fabricated as shown in the micrograph of FIG. 11A.Furthermore, FIGS. 14-18 summarize test data and system specificationsof an integrated ESR transceiver chip like the one shown in FIG. 11.FIG. 14B shows measured tuning range data for the VCO described above inFIG. 9B and implemented as shown in FIG. 11A.

As briefly described above in reference to FIG. 2, the integrated ESRtransceiver chip may be employed as part of an ESR spectrometer systemin accordance with one or more embodiments. FIGS. 12A-12B show a moredetailed diagram of an ESR spectrometer 1201 that employs an integratedESR transceiver chip 1203 like the one described above in reference toFIGS. 9-10. The functional details of an integrated ESR system havealready been described above in reference to FIGS. 1A-1B and FIG. 7 andwill not be reproduced here. However, the integrated ESR system shown inFIGS. 12A-12B differs from that described, e.g., in FIG. 7 because itemploys an integrated resonator 1200 that includes a transmitter coil1200 a and a receiver coil 1200 b. As already described in detail abovein reference to FIGS. 9-10, the ESR transceiver chip 1203 includes anintegrated transmitter circuit 901 and an integrated receiver circuit1001. In this example, integrated ESR system includes externalelectromagnet 1211 for providing B₀. A sample 1213 may be located nearthe integrated resonator 1200.

FIG. 12B shows a more detailed view of the elements of the integratedESR system in accordance with one or more embodiments. In this example,the PA circuit 1215 of the transmitter circuit converts the input RFpower from the VCO to a current in the transmitter coil 1200 a. Thiscurrent generates the RF magnetic field pulse (B₁ pulse) that may beused to manipulate the spins of the unpaired electrons in the sample.After the B₁ pulse, the PA and its pre-driver buffer are switched off toallow the receiver circuit 1209 to sense the ESR signal. In accordancewith one or more embodiments, the PA may employ an output matchingnetwork that is optimized using on chip-transmission lines. Inaccordance with one or more embodiments, the top metal layers havingrelatively low sheet resistances (0.007Ω/□ for AM and 0.37Ω/□ for MQ)may be used for the ESR resonator coils 1200 a and 1200 b in order tomaximize the quality factor of the resonator. Furthermore, the coil sizemay be 20 μm and thus, the coil may produce a B₁ field of 20 G with anexcitation current of 16 mA. Like the system described above inreference to FIG. 7, in accordance with one or more embodiments, the ESRsystem shown in FIGS. 12A-12B may operate in pulse or CW mode.

FIG. 19A shows an example ESR spectrum obtained using the CW ESR methodas described above with a 50 mg room temperature sample of2,2-diphenyl-1-picrylhydrazyl (DPPH), which is a powder composed ofstable free-radical molecules commonly used as a standard for positionand intensity of ESR measurements. In this measurement, the Zeemanmagnetic field B₀ is swept from 330 G to 352 G. The VCO frequency iskept constant at 954 MHz, which is the resonance frequency of theloop-gap resonator in this example. In this example, the integratedtransmitter sent an optimum power of 2 dBm to the resonator withoutsaturating the ESR signal. This amount of RF power generates about 0.6 Gmagnetic field at the center of the resonator. B₀ is further modulatedby a 2 kHz signal with 0.27 G amplitude to reduce the Flicker (1/f)noise. The response curve in FIG. 19A is the first-derivative of theLorentzian absorption line. FIG. 19B shows the results of a similarexperiment using Fe₃O₄ nanoparticles.

FIG. 20 shows a method of obtaining an ESR signal from a biologicalsample in accordance with one or more embodiments. Generally speaking,this method may be used in conjunction with known methods and systemsfor obtaining a magnetic resonance image from an ESR signal. For thesake of conciseness, these known systems and methods for obtaining animage from an ESR signal will not be reproduced here. In accordance withone or more embodiments, the method shown in FIG. 20 may be employedthrough the use of an integrated ESR spectrometer system that employs anintegrated ESR transceiver as described above in reference to FIGS.1-19. Furthermore, when employed in the context of an ESR imagingsystem, the integrated ESR system described above may be adapted toinclude, e.g., one or more gradient coils, computers, processors,memory, displays, user interface devices, etc. that are commonlyemployed with an ESR imaging system. General background informationregarding ESR imaging may be found in J. A. Weil et al., “ElectronParamagnetic Resonance: Elementary Theory and Practical Applications,”New York: John Wiley & Sons, Inc. 1994.

Returning to FIG. 20, in step 2001, an integrated oscillator circuitgenerates an oscillating output signal. In accordance with one or moreembodiments, the integrated oscillator circuit may be an integratedvoltage controlled oscillator circuit similar to those described abovein reference to FIGS. 2, 4A, 4B, 9A, 9B, 14A, 14B, and FIGS. 18A-18B. Instep 2003, an integrated power amplifier (PA) circuit receives theoscillating output signal from the oscillator circuit and generates anamplified oscillating output signal. In accordance with one or moreembodiments, the PA circuit may be similar to those described above inreference to for the PA circuit described in FIGS. 2, 4A, 4B, 9C, andFIGS. 18A-18B. For example, in one embodiment, the PA circuit mayamplify the oscillating output signal by 15 dB.

In accordance with one or more embodiments, the amplified oscillatingoutput signal is a current signal used to drive a transmitting resonatorused to generate an oscillating transverse magnetic field in an ESRprobe, as described above in reference to FIGS. 1A-1B, 7A-7C, and12A-12B. Furthermore, in accordance with one or more embodiments, abiological sample, or more precisely a magnetic species located within abiological sample, may be excited by the oscillating transverse magneticfield from the probe. As a result of the excitation of the biologicalsample, the magnetic species within the sample emit an ESR signal. Inaccordance with one or more embodiments, the excitation may be a CWexcitation for frequency domain imaging or may be a pulsed excitationfor time-domain imaging.

Optionally, if a pulsed excitation is used, the method may also includegenerating a voltage pulse sequence using an integrated programmablepulse generator circuit as described above in reference to FIG. 3.Furthermore, the pulsed amplified output signal may be generated byswitching the PA circuit and/or an RF buffer circuit. The PA circuit maybe switched by supplying the voltage pulse sequence to an NMOSFET driverthat is configured to pull down a base voltage of an input transistor ofthe PA circuit. This process is described in more detail above inreference to FIGS. 4B and 9A-9D and results in a very quick switchingprocess, e.g., approximately 1 ns in accordance with one or moreembodiments. Accordingly the method disclosed herein is suitable for ESRmedical applications that may use magnetic species or spin markers thathave a short relaxation time.

Returning to FIG. 20, in step 2005, the ESR signal emitted by themagnetic species of the biological sample detected by an integratedreceiver of the integrated ESR transceiver chip. More specifically, inaccordance with one or more embodiments, the integrated receiverincludes an integrated receiver amplifier that is electrically connectedto a receiving resonator of the ESR probe. The receiving resonatorreceives the ESR signal that is emitted by the sample and this ESRsignal is then is directed to an integrated receiver amplifier where itis amplified. In accordance with one or more embodiments, the receivingresonator may be the same resonator as the transmitting (excitation)resonator, known as a duplex configuration. Such a configuration isdescribed above in more detail in reference to FIGS. 7B-7C. Furthermorein accordance with one or more embodiments, the method may employ anactive leakage cancellation scheme as described above in reference toFIG. 8. In other embodiments, the receiving and transmitting resonatorsmay be separate resonators. Further embodiments may employ separateresonators that are also integrated into the integrated ESR transceiverchip, as described in more detail above in reference to FIGS. 11A-12B.Furthermore, in accordance with one or more embodiments, the integratedreceiver amplifier may be a LNA circuit like those described in FIGS. 2,5A-5B, 10A-10C, and 18A-18B. For example in accordance with one or moreembodiments, the LNA may have an noise figure of 3.7 dB and a power gainof 40 dB.

In step 2009, the amplified ESR signal is down-converted in thefrequency domain to a baseband signal. As described above in referenceto FIGS. 2, 5, and 10, this down-conversion is accomplished by way of anintegrated mixer circuit.

In step 2011, the down-converted baseband signal is sent to a integratedbaseband amplifier circuit for amplification. In accordance with one ormore embodiments, the integrated baseband amplifier may be like thosedescribed in more detail above in reference to FIGS. 2, 5, and 10.

In accordance with one or more embodiments, the integrated oscillatorcircuit, the integrated PA circuit, the integrated receiver amplifiercircuit, the integrated mixer circuit, the integrated baseband amplifiercircuit, and the integrated programmable pulse generator circuit may bedisposed on the same chip substrate, thereby forming an integrated ESRtransceiver chip. Examples of such devices fabricated using a 0.13 μmSiGeBiCMOS process are shown in the micrographs of FIGS. 6A and 11A.

In accordance with one or more embodiments, the ESR signals obtainedusing the above method have a number of uses in the biomedical arena.Generally speaking an ESR signal from a biological sample includesinformation regarding a number of physical properties of the biologicalsample. As used herein, the term biological sample is used broadly torefer to any sample that is of interest in biology or medicine and mayinclude solid, liquid, and gaseous samples. For example, biologicalsamples may include tissue samples, tumors, or tumor samples, orphantoms that include one or more biological molecules mixed within.

Generally speaking, one or more embodiments of the ESR system and methodmay detect any magnetic species within the biological sample, e.g.,para- or dia-magnetic molecules, atoms, ions, free radicals, and/ornanoparticles. A few examples of possible applications of the methodwill be described below for the sake of example. Accordingly, the systemand/or method described above should not be limited to only theseexamples.

In accordance with one or more embodiments, the biological sample may beenhanced with nanoparticles that exhibit a high ESR response. Such aparticle is known as a marker nanoparticle and/or a spin markernanoparticle. For example, FIG. 19B shows an example ESR spectrumobtained using the CW ESR method as described above with a sample ofFe₃O₄ nanoparticles. In this measurement, the Zeeman magnetic field B₀is swept from 330 G to 3300 G. The VCO frequency is kept constant at 954MHz, which is the resonance frequency of the loop-gap resonator in thisexample. In this example, the integrated transmitter sent an optimumpower of 2 dBm to the resonator without saturating the ESR signal. Thisamount of RF power generates about 0.6 G magnetic field at the center ofthe resonator. B₀ is further modulated by a 2 kHz signal with 0.27 Gamplitude to reduce the Flicker (1/f) noise. The response curve in FIG.19B is the first-derivative of the Lorentzian absorption line.

Furthermore, in accordance with one or more embodiments, thenanoparticles may be functionalized so that these nanoparticles may bedirected to particular cells of interest within the biological sample.For example, functionalized super paramagnetic iron oxide nanoparticles(SPIONs) may be used in accordance with one or more embodiments.Furthermore, any type of nanoparticle marker may be used withoutdeparting from the scope of the present disclosure.

As an additional example, the integrated ESR system and method inaccordance with one or more embodiments may be used to obtain ESR imagesof spin labeled biological samples that in turn may be used to determinethree-dimensional biomolecule conformations (e.g., proteinconformations). In addition, the ESR system disclosed herein may be usedto study the transition metal ions involved in enzymatic biochemicalpathways.

Furthermore, ESR signals obtained using the ESR system and method inaccordance with one or more embodiments may be used to study anddiagnose disease. For example, the understanding the physiologicalheterogeneity of tumors is essential for studying pathways for theinitiation and progression of cancer, the role of micro-environmentalfactors, and, in turn, the tumor-drug and tumor-radiation interaction.To that end, the ESR system and method in accordance with one or moreembodiments may facilitate quantitative, non-invasive, in vivo imagingtechniques with sufficient spatial and temporal resolution to study thecomplexity of physiological variations in tumors, and to compare andcontrast them to normal tissue. For example, the ESR signals obtainedusing the ESR system and method in accordance with one or moreembodiments, may further elucidate the role of free radicals andoxidative stress within tumors.

In addition, the ESR images may provide a quantitative, spatiallyresolved map of the oxygen distribution in solid tumor cancers. Such amap allows staging of tumors in terms of their resistance to radiationand chemotherapy because hypoxic (low oxygen molecule concentration,referred to herein as [O₂]) tumors tend to have more aggressivephenotype with higher resistance to radiation. In accordance with one ormore embodiments, the ESR system and method may be used to performoximetery based on the interaction of oxygen unpaired electrons with areporter molecule that may be an inert, biologically stable, freeradical. Some examples of such reporter molecules include carbonparticulates, e.g., India Ink, molecules with one or more nitroxidesbonds, and/or tri-aryl-methyl (trityl) molecules with a protectedelectron on the central methyl carbon. These reporter molecules aregiven here merely for the sake of example and are not intended to limitthe scope of the present disclosure. Furthermore, in accordance with oneor more embodiments, the ESR system and method operating in pulse modemay be used to measure and/or image the temporal relaxation propertiesof the reporter molecules, e.g., by measuring the ESR relaxationproperties such as T₁, T₂, and/or T₂ ^(*). Because the change in thereporter molecule relaxation rate is proportional to the localconcentration of oxygen and not the concentration of the reportermolecules themselves, ESR spectroscopy/imaging using the system andmethods disclosed herein provides an accurate estimation of tissueoxygenation.

Furthermore, depending on the type of spin marker, other physiologicalparameters of interest such as acidity, viscosity, presence of freeradicals, and temperature in tumors may be measured noninvasively andquantitatively using the ESR system and method in accordance with one ormore embodiments. In the case of cardiovascular diseases, the ESR systemmay be used to study the generation of free radicals and small signalingmolecules, e.g., nitric oxide, during various pathologies, e.g., as amechanism for ischemia reperfusion injury. In addition, because melaninpigments act as spin traps, these pigments can be detected using the ESRsystem and method thereby allowing the ESR system in accordance with oneor more embodiments to be used to detect and study melanomas. The ESRsystem in accordance with one or more embodiments may be used forstudying the superficial skin lesion in addition to metastasis to otherorgans.

In addition, one or more embodiments of the ESR system disclosed hereinmay be used to study reactions with free radicals, that may be generatedas intermediates or products. To this end, one or more embodiments ofthe ESR system may be used in a radiation dosimeter system, where thedose of ionizing radiation may be determined by ESR measurement of theamount of free radicals generated in a standardized sample, (e.g., analanine block) or in-vivo measurement of exposure to ionizing radiation(e.g., during a nuclear catastrophe) by ESR measurement of free radicalsin tooth enamels of potential victims.

In accordance with one or more embodiments, the integrated ESR systemmay be used in a system for the early detection of cancer. Accordingly,the biological sample may include magnetic nanoparticles that arefunctionalized with a cancer-specific antibody. This cancer-specificantibody causes the nanoparticles to attach to cancerous cells. The ESRsensor is then used to detect the ESR signal from the magneticnanoparticles that are attached to cancerous cells. This is becauseunlike an NMR signal, which is generated by protons in tissues, the ESRsignal is generated by the unpaired electrons that exist in nanoparticleand not in the tissue. Thus, this form of ESR based detection isextremely versatile and may be used to detect a number of differentcancers by appropriate functionalization of the nanoparticle.Accordingly, one or more embodiments of the integrated ESR systemproposed herein can be used in a non-invasive manner by usingtarget-specific functionalized nanoparticles as surrogate markers (i.e.,the integrated ESR system and nanoparticle serve as an integratedsensor-antenna reporter system).

In accordance with one or more embodiments, a magnetic nanoparticle,e.g., SPIONs, or the like, may be functionalized to detectProstate-Specific G-protein coupled Receptor (PSGR). PSGR isspecifically expressed in human prostate tissues. Furthermore, it hasbeen shown that Prostatic Intraepithelial Neoplasia (PIN) is theprecursor of prostate cancer and is marked by the overexpression(approximately 10-fold) of PSGR. Thus, in accordance with one or moreembodiments, anti-PSGR functionalization may be used to direct themagnetic nanoparticles to PIN cells and enable their detection by theESR sensor. In accordance with one or more embodiments, the ESR sensormay detect the presence, location, and concentration of PSGR. Thus, inaccordance with one or more embodiments, the system and method disclosedherein may be used for early detection of prostate cancer.

In accordance with one or more embodiments, a magnetic nanoparticle,e.g., SPIONs, or the like may be used to detect μ-Opioid expression inlung tissue. It has been recently shown that there is a 5- to 10-foldincrease in μ-Opioid expression in lung samples from patients with humanNon-Small Cell Lung Cancer (NSCLC). μ-Opioid Receptor (MOR) is animportant regulator of lung cancer progression. MOR overexpressionincreases Akt and mTOR activation, proliferation, and extravasation inhuman bronchioloalveolar carcinoma cells. Accordingly, in accordancewith one or more embodiments, MOR-expressing NSCLC can be targeted byanti-MOR-functionalized magnetic nanoparticle, e.g., a SPION, or thelike, that can serve as a magnetic beacon and indicate the presence,location, and concentration of NSCLC by an ESR sensor. Thus, inaccordance with one or more embodiments, the system and method disclosedherein may be used for early detection of lung cancer.

In accordance with one or more embodiments, cancer cells may be targetedby nanoparticles having molecular specificity towards tumor-associatedantigen (TAA). Accordingly, one or more embodiments of the inventionallow for early detection of cancers by looking at an organ of originfor pre-invasive lesions rather than the serum markers released bycancer cells. For example, pathologic analysis of prophylactic removalof the fallopian tubes and ovaries in women with increased risk, i.e.,BRCA+, has revealed a possible precursor lesion in the lumen of thedistal fimbriated end of the fallopian tube. Thus, one or moreembodiments of the ESR system may avoid the miss-classification offallopian tube cancers as ovarian cancer, and further expand theopportunities for early-detection.

Due to its small size, the integrated ESR system in accordance with oneor more embodiments of the invention may be inserted into a livingpatient, e.g., into the fallopian tube of a patient in the exampledescribed above. Accordingly, increased ESR signal may be obtained dueto the proximity of the ESR detector, e.g., the receiver resonator, tothe biological sample being investigated, in this case, e.g., apre-invasive lesion in a fallopian tube.

In accordance with one or more embodiments, the voltage amplitude of theESR signal at the receiver can be calculated by the following equation

V_(s)=χ″ηQ√{square root over (PZ₀)}

where, V_(s) is the ESR signal at the end of the transmission lineconnected to the resonator, η is the filling-factor, Q is thequality-factor of the resonator, Z₀ is the characteristic impedance ofthe transmission line, and P is the microwave power. As used herein thefilling factor η is defined as the ratio of the sample volume to thevolume of the resonator, where the cubic or spherical resonator volumeis defined to the volume bounded by a cube or sphere, respectively,centered on the resonator that has a side or diameter, respectively,that is equal to the largest dimension of the resonator. Thus, inaccordance with one or more embodiments, because the size of theintegrated sensor is several orders of magnitude smaller thanconventional spectrometers, one or more embodiments of the inventionsignificantly boosts the filling factor and the sensitivity of thedevice. For example, an integrated ESR resonator with volume of (0.1mm)×(0.1 mm)×(0.1 mm)=10⁻³ mm³ to detect 10,000 nanoparticles in asample volume of 10⁻³ mm³, the filling factor would be around 1.Conventional ESR resonators have a volume of greater than 1000 mm³,which results in a filling factor of 10⁻⁶. Accordingly, filling factorsin a range between 10⁻⁶ to 1 are realizable in accordance with one ormore embodiments. In a typical measurement, the range of filling factorsmay be 0.01-1, or 0.1-1. One of ordinary skill will appreciate that anynumber of filling factors up to 1 may be employed in accordance with oneor more embodiments without departing from the scope of the presentdisclosure. The high filling factors possible in accordance with one ormore embodiments of the present invention mean that the magnitude of theESR signal produced by the sensor in accordance with one or moreembodiments may be larger that traditional sensors by as much as afactor of 10⁶. Accordingly, one or more embodiments provides for asignificant enhancement sensitivity over traditional devices.

In accordance with one or more embodiments, because the size of ourintegrated ESR resonator is very small, it can be mounted on a tinyprobe (1 mm) and can be placed very close to the tissue. For example, inthe case of ovarian cancer, the resonator may be placed very close to acancerous tissue inside the living patient, e.g., in the ovary tomaximize the filling factor.

In accordance with one or more embodiments, a drug may be loaded into oronto the surface of a collection of magnetic nanoparticles. Thenanoparticles can then be placed in a carrier, e.g., a porous amorphoussilicon carrier with diameter of 1 μm (10⁻⁶ m). When the carrierreleases the magnetic nanoparticles, its ESR spectrum changes. This isbecause when magnetic nanoparticles are in close proximity of each-other(less than 100 nm) their magnetic field changes the ESR spectrum ofother nanoparticles. This means that the miniaturized ESR sensor can beused to monitor the quality (and occurrence) of drug delivery.

In the following figures, the measured ESR response for differentsamples with various concentrations is shown. From the measurements, itis shown that one or more embodiments of the invention may detectmagnetic nanoparticles with a concentration of as small 0.1 ppm, whichis a clinically significant number.

FIGS. 21A and 21B show the magnitude of the ESR signal (reflected powerform the resonator) taken for powder Fe₃O₄ and in a solution with only5.8% concentration of 10 nm nanoparticles Fe₃O₄, respectively.Similarly, FIGS. 22A and 22B show a similar measurement but using 30nm-50 nm Fe₃O₄ powder and 5% solution (50 mg nanoparticles/1 ml ofwater). This data shows that the integrated ESR system in accordancewith one or more embodiments can use magnetic nanoparticles todifferentiate the environment surrounding the nanoparticles, i.e., itcan probe interactions of magnetic nanoparticles with the surroundingenvironment.

FIGS. 23A and 23B show the measured ESR absorption and dispersionspectrum, respectively, for Molday Ion C6 Amine nano-particles in water.In this example a concentration of 1% was used and voltage amplitude of100 μV was achieved. Because in this example, the voltage sensitivity ofthe sensor is around 1 nV, this data shows that the sensor can measureconcentrations as small as 0.1 ppm. In accordance with one or moreembodiments, the sensor can detect an ESR signal from a small amount,e.g., 1,000 of magnetic nanoparticles that are within the resonatorvolume, where the resonator volume is defined to the volume bounded by acube or sphere centered on the resonator are having a side or diameter,respectively that is equal to the largest dimension of the resonator.For example, for a square loop-gap resonator having an outer diameter of5 mm, the spherical resonator volume would be the volume of a spherehaving a diameter of 5 mm that is centered on the resonator. Likewise,the cubic resonator volume would be defined to be a cube centered on theresonator and having a sides of length 5 mm.

FIGS. 24A and 24B show the measured ESR absorption and dispersionspectrum, respectively, for a nitroxy sample in accordance with one ormore embodiments.

In accordance with one or more embodiments, due to the high sensitivityof integrated ESR sensor, it can be used it in conjunction with apermanent magnet, e.g., a rare earth magnet to measure the ESR signal. Arare earth magnet has a large gradient of the magnetic field, whichreduces the amplitude of the signal. However, due to the highsensitivity of the sensor, the ESR signal may still be measured from adistance of several cm.

Accordingly, in accordance with one or more embodiments, a portable ESRsystem may be made using one or more permanent magnets, e.g., rare-earthmagnets placed sideways in a robust setup with an inductor serving asthe modulation coil. One of ordinary skill will appreciate that manydifferent configurations of permanent magnets may be used withoutdeparting from the present disclosure, e.g., a Halbach array or thelike. FIG. 25 shows an example of the ESR system in accordance with oneor more embodiments. The sensor may include an integrated ESRtransceiver chip (not shown) like that shown and described in detailabove in reference to FIGS. 1-20. The ESR system shown in FIG. 25 isfunctionally similar to that shown and described above in reference toFIG. 1A in that it is configured to operate in the CW mode in accordancewith one or more embodiments. In this example, a sinusoidal RF signal2503 (the amplified oscillating output signal) is sent to the resonator2509 and reflected RF power 2517 that is reflected from the resonator ismeasured to calculate the amount of the RF power absorbed by the sample2513. The absorbed power varies with the strength of the B₀ field andthus, the RF power absorption curve, reflected in the reflected RF power2517 as a function of B₀, reveals the magnetic properties of the sample2513. In accordance with one or more embodiments, in order to reduce thelow frequency noise (1/f), B₀ may be modulated at a frequency f_(CW) andthe reflected power 2517 may be measured at the same modulationfrequency f_(CW). Furthermore, in accordance with one or moreembodiments, the B₀ field may be held constant and the RF frequency ofthe sinusoidal RF signal 2503 may be modulated to perform the CWmeasurement.

In accordance with one or more embodiments, B₀ may be provided by asmall permanent magnet 2519, e.g., a rare earth magnet. Furthermore, themodulation of B0 may then be applied by sending an oscillating currentthrough the modulation coil 2521. In this example, the sample 2513 maybe located close to the resonator 2509. In accordance with one or moreembodiments, the sample 2513 may be a biological sample, e.g., a humantissue, and may include one or more magnetic nanoparticles 2525, e.g.,SPIONs, or the like. Furthermore, in accordance with one or moreembodiments, the magnetic nanoparticles 2525 may be functionalized suchthat it may bind to a certain type of cell 2527, as described above. Forexample, if the nanoparticle may be functionalized with a certaintumor-associated antigen (TAA) such that the nanoparticle will bedirected to a certain type of tumor cell. In accordance with one or moreembodiments, the magnetic nanoparticle may be functionalized with theappropriate anti-receptor molecule, e.g., anti-μ-Opioid Receptor,anti-Prostate-Specific G-protein coupled Receptor, or any otherappropriate functionalization. In accordance with one or moreembodiments, the ESR signal of the magnetic nanoparticle may be detectedby the integrated ESR transceiver ship and thus, the functionalizedmagnetic nano-particle may serve as an antenna or marker for certainbiological molecules.

While the above portable ESR system is described in the context of a CWmeasurement that employs functionalized nanoparticles the device may beemployed to do time domain ESR measurements as well. Furthermore, thesystem may be implemented using the integrated ESR transceiver chip thatinclude an integrated resonator as described in detail above withoutdeparting from the scope of the present disclosure.

FIG. 26 shows a photograph of one example of the portable system inaccordance with one or more embodiments. The system 2601 is located nextto a common ball point pen 2603 to give a sense of scale. A planarloop-gap resonator 2605 is shown connected to a board 2607 whichimplements interconnects to the integrated ESR transceiver chip 2609.The size and scale of the example shown here is not intended to limitthe scope of the present disclosure but is shows as merely one example.

FIGS. 27A-27B show test data in accordance with one or more embodimentsof the invention. FIG. 27A shows the detected ESR signal for a sample ofFe₃O₄ nanoparticles as a function of distance between the sample and thefront surface of a permanent magnet. This measurement uses a fixeddistance between a resonator and a sample. In this measurement, the lineof displacement for the measurement is a line connecting the center ofthe resonator to the center of the magnet and is almost normal to thesurface of the planar magnet. At the peak point, the sample is locatedat a position in space where the magnetic field generated by thepermanent magnet is close to 350 Gauss, which is the field required toproduce an strong ESR signal in the nanoparticle sample with a resonancefrequency of around 1 GHz.

FIG. 27B shows the magnetic field as a function of distance from thesame permanent magnet used to take the data shown in FIG. 27A. Thismeasurement is used to calibrate the magnetic field of the permanentmagnet. As expected, the magnetic field drops as a function of thedistance from the magnet.

FIGS. 28A-28C show test data in accordance with one or more embodimentsof the invention. FIG. 28A shows the detected ESR signal for a varyingdistance (from 0 mm to 5 mm) between a resonator and a sample. In thismeasurement, the position of both the sample and the permanent magnet isfixed. To make the measurement, the resonator is moved away from thesample to reduce the filling factor. By reducing the filling factor, themagnitude of the ESR signal is correspondingly reduced. FIG. 28B showsthe same measurement but over a larger scale of displacement (from 0 mmto 35 mm). FIG. 28C shows a similar measurement made using a resonatorthat is different from the resonator used to take the data shown inFIGS. 28A-28B. Both resonators are flat loop-gap made in-house using a20 mil Rogers 4350B PCB. The loop has inner and outer diameters of 4 mmand 5 mm, respectively

FIG. 29 shows a measured ESR signal as a function of displacement alonga direction that is parallel to the front face of the permanent magnetand perpendicular to the table surface of the test bench. In thismeasurement, the surface of the magnet and the surface of the table arenormal to each other. The distance between the center of the resonatorand the center of the magnet can be calculated by ((4.5 cm)²+X²)^(1/2),where the displacement X is shown on the horizontal axis in this figure.Several different separations between a sample and a resonator areshown. This measurement is performed with five differentresonator-sample spacings: 0.1 mm, 0.5 mm, 1 mm, 3 mm, 5 mm.

FIGS. 30A-30B show a measured ESR signal as a function of displacementbackward (30A) and forward (30B) along a direction that is parallel tothe front face of the permanent magnet and parallel to the table surfaceof the test bench. In this measurement, the surface of the magnet andthe table are normal to each other. The distance between the center ofthe resonator and the center of the magnet can be calculated from thisequation ((4.5 cm)²+Y²)^(1/2), where the displacement Y is shown on thehorizontal axis in this figure. This measurement is performed with threedifferent resonator-sample spacings: 1 mm, 3 mm, 5 mm.

FIGS. 31A-31B show results of a characterization of the magnetic filedproduced by the permanent magnet used to produce the data of FIGS.27-30. The magnetic field strength is measured as a function of distancefrom the front face of the permanent magnet for 5 different positionsrelative to the front face of the magnet, labeled 1-5 in FIG. 31A. Themeasurement is performed with starting points chosen at the center (1),top right corner (2), bottom right corner (3), top left corner (4), andbottom left corner (5) of the square planar magnet. In all of thesemeasurement, the probe of the Gauss meter is moved away from the magneton a line that is substantially perpendicular to the surface of themagnet.

FIG. 32 show a plot of the strength of the magnetic field produced bythe permanent magnet used to produce the data of FIGS. 27-30.

The test data shown in FIGS. 27-32 are shown merely for the sake ofexample and are not intended to limit the scope of the presentdisclosure in any way. It can be appreciated that the above measurementsand characterizations can be repeated with any type of magnet (includingan electromagnet), resonator, and sample. Accordingly the particularstructure of the integrated ESR system used to perform thesesmeasurement is not intended to limit the scope of the presentdisclosure.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

What is claimed is:
 1. A method of obtaining an electron spin resonance(ESR) signal from a biological sample using an integrated electron spinresonance circuit chip having a chip substrate, the method comprising:generating, from an integrated oscillator circuit, an oscillating outputsignal; generating, by an integrated power amplifier (PA) circuit, anamplified oscillating output signal based on the oscillating outputsignal; and receiving, by integrated receiver amplifier circuit, an ESRsignal from the biological sample that includes a magnetic species;generating, by the integrated receiver amplifier circuit, an amplifiedESR signal based on the received ESR signal; down-converting, by anintegrated mixer circuit, the amplified ESR signal to a baseband signal;and generating, by an integrated baseband amplifier circuit, anamplified baseband signal based on the baseband signal, wherein theintegrated oscillator circuit, the integrated PA circuit, the integratedreceiver amplifier circuit, and integrated mixer circuit, and theintegrated baseband amplifier circuit are all disposed on the chipsubstrate.
 2. The method of claim 1, wherein the magnetic species is oneselected from a group consisting of a molecule, an atom, an ion, a freeradical, and a nanoparticle.
 3. The method of claim 2, wherein themagnetic species is a nanoparticle and the nanoparticle is a superparamagnetic iron oxide nanoparticle (SPION).
 4. The method of claim 1,wherein the magnetic species comprises a reporter molecule thatinteracts with a magnetic molecule in the biological sample.
 5. Themethod of claim 4, wherein the magnetic molecule is Oxygen (O₂).
 6. Themethod of claim 5, wherein the reporter molecule is one selected for agroup consisting of carbon particulate, a molecule with a nitroxidesbond, and a tri-aryl-methyl (trityl) molecule with a protected electronon the central methyl carbon.
 7. The method of claim 4, wherein arelaxation rate of the reporter molecule is proportional to aconcentration of the magnetic molecule in the biological sample.
 8. Themethod of claim 7, wherein the relaxation rate is one selected from agroup consisting of T₁ relaxation rate, T₂ relaxation rate, and T₂ ^(*)relaxation rate.
 9. The method of claim 1, wherein generating theamplified oscillating output signal further comprises pulsing theamplified output signal to excite a time domain ESR signal in thebiological sample.
 10. The method of claim 9, wherein pulsing theamplified output signal includes: generating, by an integrated digitalpulse generator circuit, a voltage pulse, wherein the integrated digitalpulse generator circuit is disposed on the chip substrate.
 11. Themethod of claim 10, further comprising: providing the voltage pulse to agate terminal of a switching transistor to switch the amplifiedoscillating output signal, wherein the switching transistor is connectedto an input terminal of the PA circuit.
 12. The method of claim 11,further comprising pulling down a bias voltage of an input transistor ofthe PA circuit to switch the amplified oscillating output signal inresponse to the voltage pulse from the integrated digital pulsegenerator circuit.
 13. The method of claim 9, wherein the time domainESR signal is an electron spin relaxation signal.
 14. The method ofclaim 14, wherein the electron spin relaxation signal providesinformation related to one selected from a group consisting of T₁, T₂,and T₂ ^(*).
 15. The method of claim 1 wherein the magnetic species is afree radical generated by exposing the biological sample to ionizingradiation.
 16. The method of claim 1, wherein the biological sample isan alanine (CH₃CH(NH₂)COOH) phantom.
 17. The method of claim 1, whereinthe magnetic species is a melanin pigment molecule.
 18. The method ofclaim 1, wherein the biological sample a tissue sample.
 19. The methodof claim 18, wherein the tissue sample originates from a tumor.
 20. Themethod of claim 1, wherein the ESR signal is used in early detection ofcancer. In this application, magnetic nanoparticles can befunctionalized with a cancer specific antibody. The antibody causes thenanoparticles to attach to cancerous cells. The ESR sensor is then usedto detect the cancerous cells that are attached to magneticnanoparticles.
 21. The method of claim 1, wherein the ESR signal is usedto monitor drug delivery. In this application, various drugs can beloaded to magnetic nanoparticles. These nanoparticles can be placed in acarrier (such as a porous amorphous silicon with diameter of 1 um). Whenthe carrier releases the magnetic nanoparticles, its ESR spectrumchanges. This is because when magnetic nanoparticles are in closeproximity of each-other (less than 100 nm) their magnetic field changesthe ESR spectrum of the other nanoparticles.
 22. The method of claim 1,wherein the integrated ESR circuit chip is disposed within a patient atleast during a time the ESR signal is obtained.
 23. The method of claim22, wherein the integrated ESR circuit chip is disposed within an ovaryof the patient.
 24. The method of claim 22, where in the biologicalsample comprises the patient's tissue.
 25. The method of claim 1,wherein a filling factor of a resonator used to detect the ESR signal issubstantially
 1. 26. The method of claim 1, wherein a filling factor ofa resonator used to detect the ESR signal is from 0.1 to
 1. 27. A methodof detecting an electron spin resonance (ESR) signal, the methodcomprising: exciting a magnetic nanoparticle that is functionalized witha cancer specific antibody using an oscillating magnetic field, whereinthe oscillating magnetic field causes the magnetic nanoparticle to emitan ESR signal; and receiving the ESR signal.
 28. The method of claim 26,wherein the oscillating magnetic field is generated by an amplifiedoscillating output signal for an integrated electron spin resonancecircuit chip having a chip substrate, the method further comprising:generating, from an integrated oscillator circuit, an oscillating outputsignal; generating, by an integrated power amplifier (PA) circuit, theamplified oscillating output signal based on the oscillating outputsignal; and receiving, by integrated receiver amplifier circuit, the ESRsignal; generating, by the integrated receiver amplifier circuit, anamplified ESR signal based on the received ESR signal; down-converting,by an integrated mixer circuit, the amplified ESR signal to a basebandsignal; and generating, by an integrated baseband amplifier circuit, anamplified baseband signal based on the baseband signal, wherein theintegrated oscillator circuit, the integrated PA circuit, the integratedreceiver amplifier circuit, and integrated mixer circuit, and theintegrated baseband amplifier circuit are all disposed on the chipsubstrate.
 29. The method of claim 26, wherein the cancer specificantibody is anti-Prostate-Specific G-protein coupled Receptor.
 30. Themethod of claim 26, wherein the cancer specific antibody isanti-μ-Opioid Receptor.
 31. The method of claim 26, wherein theintegrated ESR circuit chip is disposed within a patient at least duringa time the ESR signal is obtained.
 32. The method of claim 27, whereinthe integrated ESR circuit chip is disposed within an ovary of thepatient.
 33. The method of claim 27, where in the biological samplecomprises the patient's tissue.
 34. The method of claim 27, wherein afilling factor of a resonator used to detect the ESR signal issubstantially
 1. 35. The method of claim 27, wherein a filling factor ofa resonator used to detect the ESR signal is from 0.1 to
 1. 36. A methodof detecting an electron spin resonance (ESR) signal, the methodcomprising: exciting a magnetic nanoparticle, wherein the magneticnanoparticle comprises a drug, and the magnetic nanoparticle is disposedwithin a carrier, wherein the oscillating magnetic field causes themagnetic nanoparticle disposed within the carrier to emit an ESR signal;and receiving the ESR signal from the magnetic nanoparticle disposedwithin the carrier.
 37. The method of claim 36, wherein the oscillatingmagnetic field is generated by an amplified oscillating output signalfor an integrated electron spin resonance circuit chip having a chipsubstrate, the method further comprising: generating, from an integratedoscillator circuit, an oscillating output signal; generating, by anintegrated power amplifier (PA) circuit, the amplified oscillatingoutput signal based on the oscillating output signal; and receiving, byintegrated receiver amplifier circuit, the ESR signal; generating, bythe integrated receiver amplifier circuit, an amplified ESR signal basedon the received ESR signal; down-converting, by an integrated mixercircuit, the amplified ESR signal to a baseband signal; and generating,by an integrated baseband amplifier circuit, an amplified basebandsignal based on the baseband signal, wherein the integrated oscillatorcircuit, the integrated PA circuit, the integrated receiver amplifiercircuit, and integrated mixer circuit, and the integrated basebandamplifier circuit are all disposed on the chip substrate.
 38. The methodof claim 36, wherein the carrier is porous amorphous silicon carrier.39. The method of claim 36, wherein the integrated ESR circuit chip isdisposed within a patient at least during a time the ESR signal isobtained.
 40. The method of claim 36, wherein a filling factor of aresonator used to detect the ESR signal is substantially
 1. 41. Themethod of claim 36, wherein a filling factor of a resonator used todetect the ESR signal is from 0.1 to 1.